Possible merger signatures of the bulges of non-dwarf galaxies in the core of the Coma Cluster

Abstract

In this paper, we discuss a method to study virialised clusters of galaxies with no-interaction features, like tails and bridges, using diagnostics of bulge classification and their properties, namely Sérsic index (n) and the Kormendy relation. We study a sample of non-dwarf galaxies in the core of the Coma Cluster using HST/ACS data. We divided our galaxy sample into 4 categories based on bulge to total light ratio (B / T): B / T < 0 . 3 (12%), 0 . 3 < B / T ≤ 0 . 6 (38%), 0 . 6 < B / T ≤ 0 . 8 (29%) and B / T > 0 . 8 (21%). We classified the galaxy bulges using Sérsic index (n) and the Kormendy relation, where classical bulges are a result of mergers and pseudo bulges are a result of secular evolution. Using Sérsic index we found that 75% galaxies in our sample had classical bulges (n > 2) and 25% galaxies had pseudo-bulges (n < 2). From the Kormendy diagram we found that 90% galaxies had classical and 10% galaxies had pseudo-bulges. We observed that classical bulges with B / T ≥ 0 . 3 galaxies in the central region of Coma Cluster (within 0.4 Mpc from NGC 4874) are redder in colour (F 475 W - F 814 W ≥ 1 . 17). Pseudo-bulges and B / T ≤ 0 . 3 galaxies are within 0.6 to 1.1 Mpc from NGC 4874 and are bluer in colour (F 475 W - F 814 W ≤ 1 . 13). We find that the majority of galaxies with classical bulges have B / T ≥ 0 . 3 and those with pseudo-bulges have B / T ≤ 0 . 3 . With our study of the Kormendy relation and colour, B / T and distance from centre relations, we infer that galaxies in the central region of Coma Cluster with B / T ≥ 0 . 3 may have formed by mergers and those with B / T ≤ 0 . 3 may have formed by secular process.